The present invention relates to a microminiature movable device and, more particularly, to a microminiature movable device in which an auxiliary electrode is formed on a stationary substrate together with a stationary electrode to prevent a movable electrode plate from sticking or adhering to the stationary substrate.
To facilitate a better understanding of the present invention, a description will be given first, with reference to FIGS. 1A and 1B, of a prior art example of a microminiature movable device.
The illustrated microminiature movable device is manufactured using a silicon (Si) single crystal wafer as the starting substrate through application of micromachining technology including thin-film growth, photolithography and etching techniques. The silicon single crystal wafer is ultimately machined into such a square support frame 10 as depicted in FIGS. 1A and 1B. The support frame 10 has formed integrally therewith anchor parts 11 located centrally on a pair of opposed sides of the frame, flexures 19 extended inwardly from the anchor parts 11 and a rectangular movable electrode plate 12 connected centrally at its both sides to inner ends of the flexures 19.
On the top of the movable electrode plate 12 there are formed four micro-nirrors 13 having their reflecting surfaces held perpendicular to the movable electrode plate 12. Reference numeral 10a denotes a countersink bored through the support frame 10. Fixedly mounted on the underside of the support frame 10 in a manner to cover the countersink 10a is a stationary electrode substrate or plate 80 with a film-formed stationary electrode 84 on the top thereof, the stationary electrode plate 80 being in spaced parallel relation to the movable electrode plate 12. Reference numerals 14 and 14xe2x80x2 denote output optical fibers or optical waveguides, and 15 and 15xe2x80x2 denote input optical fibers or optical waveguides. Incidentally, FIGS. 1A and 1B show the case where the miniature movable device is an optical switch.
Now, the operation of the optical switch will be described below with reference to FIGS. 2A to 2D.
Referring first to FIGS. 2A and 2B, light transmitted over the input optical fibers 14 and 14xe2x80x2 is emitted from their end faces, and propagate through the space to the micro-mirrors 13, by which it is reflected for incidence on the output optical fibers 15 and 15xe2x80x2. This state will hereinafter referred to as a steady state.
Turning next to FIGS. 2C and 2D, when a voltage is applied across the stationary electrode 84 and the movable electrode plate 12 to generate therebetween static electricity in a direction in which they attract each other, the movable electrode plate 12 is driven downwardly, by which the flexures 19 are elastically deformed, and consequently, the movable electrode plate 12 is displaced downward. The micro-mirrors 13 formed on the top of the movable electrode plate 12 are also displaced downward, and hence they go down below the optical paths of the light emitted from the end faces of the input optical fibers 14 and 14xe2x80x2. In this case, the light emitted from the end face of the input optical fiber 14 is no longer intercepted by the micro-mirrors 13, and it travels in a straight line and impinges on the output optical fiber 15xe2x80x2. Similarly, the light emitted from the light emitted from the end face of the input optical fiber 14xe2x80x2 strikes on the output optical fiber 15. In this way, the optical paths to the output optical fibers 15 and 15xe2x80x2 can be switched spatially without using solid optical waveguides as of transparent synthetic resin.
In the above-described microminiature movable device, the movable electrode plate 12 and the flexures 19 are both so thin, in general, that they are small in their elastic restoring force. And, the underside of the movable electrode plate 12 is smooth, whereas the top of the stationary electrode 84 is also smooth and is stained and moist as well, allowing polarization in the electrode surface and generating van der Waals forces, too. Under these conditions, when the movable electrode plate 12 is displaced downward to bring its underside into contact with the top of the stationary electrode 84, they adhere to each other and do not separate immediately, sometimes disturbing smooth switching operation. Incidentally, such adhesion can be avoided, for example, by roughening either one or both of the underside surface of the movable electrode plate 12 and the top surface of the stationary electrode 84. However, roughening either one or both of the two contacting surfaces involves some additional process steps, and hence it introduces complexity in the manufacture of the microminiature movable device.
It is therefore an object of the present invention to provide a microminiature movable device adapted so that the movable electrode plate, when brought into contact with the stationary electrode, can be separated therefrom relatively easily.
The microminiature movable device according to the present invention comprises:
A microminiature movable device comprising:
a stationary electrode substrate having a centrally-disposed protrusion with a stationary electrode formed on its top;
auxiliary electrode means formed on said stationary electrode substrate at a position adjacent said protrusion and at a level lower than said stationary electrode;
a movable electrode part having an area opposite said stationary electrode and said auxiliary electrode means;
at least two flexures resiliently supporting at one end said movable electrode part at at least two places of its marginal edge; and
a support frame secured to said stationary electrode substrate, for fixedly supporting the other ends of said flexures to hold said movable electrode plate so that it can be engaged with or disengaged from said stationary electrode.